1. Field of the Invention
This invention pertains to the field of conversion of diols to lactones by oxidation in the presence of a catalyst. More particularly, it relates to the improved production of lactones at low temperatures utilizing ruthenium containing catalysts.
II. Description of the Prior Art
It is known to convert diols to lactones by heating the diol in the presence of a copper chromite catalyst. See, for example, Ulmanns Encyclopedia of the Chemical Industry, Vol. A4, p. 495-498. The general reaction sequence using a butane-1,4-diol as starting material, is as follows: ##STR1##
The major problem, however, with this reaction is that it requires excessively high temperatures, namely, temperatures in excess of 200.degree. C. Consequently, if one is preparing a lactone which is thermally sensitive, the high temperature of preparation severely inhibits or renders impossible the carrying out of the dehydrogenation reaction since any product which is formed is destroyed.
It has also been reported that soluble, homogeneous ruthenium complexes can promote dehydrogenation of 1,4-diols if appropriate hydrogen acceptors are present. S. Murahashi, et al., J. Org. Chem., 1987, 52, 4319. ##STR2##
These reactions also require elevated temperatures, e.g., 120-200.degree. C., in order to process at reasonable rates. Also, the catalysts are quite expensive.
It is also known that ruthenium tetroxide is capable of acting as a stoichiometric oxidant for converting alcohols to ketones, aldehydes to acids and ethers to esters or lactones. It is further known that ruthenium can be used in catalytic amounts in the form of ruthenium trichloride or ruthenium oxide if used with an oxidant, such as, sodium hypochlorite to convert ethers to esters. (See "Metal-Catalyzed Oxidations of Organic Compounds" by R.A. Sheldon and J.K. Kochi, Academic Press (1981), Chapter 12.) Indirect electrooxidation of alcohols and diols to acids and lactones, respectively, has been reported using ruthenium-based catalyst system. This was accomplished by utilizing a double mediating system of RuO.sub.4 /RuO.sub.2 and C1.sup.+ /C1.sup.- redoxes in an aqueous-organic two-phase system. See J. Org. Chem., 1986, 51, p. 155-161.